1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device which has a copper metal layer that is a metal layer mainly containing copper.
2. Description of the Related Art
Conventionally, it is difficult to etch a copper metal. This imposes the use of a damascene-based wire forming technique for copper metal layers, unlike the formation of wires by etching aluminum. The damascene method is disclosed, for example, in JP-2001-156168-A in the following manner. After grooves are formed in an insulating film for wiring, a barrier metal, later serving as a barrier layer for preventing copper from diffusing, a seed layer, and a copper metal layer are formed in order. Subsequently, a copper grain growth annealing is performed for growing grains of copper, followed by CMP (Chemical and Mechanical Polishing) processing to polish the copper metal layer until the insulating film is exposed, and copper wires are formed in the grooves.
Next, description will be made on the grain growth process in the copper metal layer in the prior art technique mentioned above.
FIGS. 1A to 1C are cross-sectional views of a structure for showing a grain growth process in a copper metal layer, and an oxidation process in a barrier metal.
As illustrated in FIG. 1A, a barrier metal composed of tantalum nitride (TaN) film 112 and tantalum (Ta) film 114 is formed on interlayer insulating film 110 deposited on a semiconductor substrate, not shown. Subsequently, a seed layer and copper metal layer 116 are formed on the barrier metal. As copper metal layer 116 is exposed to the atmosphere after the formation, the surface of copper metal layer 116 is oxidized to form copper oxide 118 on the surface of copper metal layer 116, as illustrated in FIG. 1A.
Subsequently, as copper grain growth annealing is started for growing grains of copper, grain interfaces 120 occur as more grains of copper grow, as illustrated in FIG. 1B. Afterwards, as the growth of copper grains approaches the end, oxygen contained in copper oxide 118 diffuses toward the barrier metal along grain interfaces 120, as illustrated in FIG. 1C. As the oxygen reaches the barrier metal, a tantalum oxide compound is produced on the bottom of copper metal layer 116 because tantalum is more susceptible to oxidization than copper. The principles of producing a tantalum oxide compound are shown in literature of K.Yin et al., xe2x80x9cOxidization of Ta diffusion barrier layer for Cu metallization in thermal annealing/Thin Solid Films,xe2x80x9d 388 (2001), pp. 27-33.
The tantalum oxide compound may give rise to the following problems.
Copper oxide 118 remaining on copper metal layer 116 is removed in the subsequent CMP processing. On the other hand, the tantalum oxide compound formed on the interface between the barrier metal and copper metal layer 116 still remains within the subsequently formed wires. The residual tantalum oxide compound degrades the adhesivity of copper metal layer 116 to the barrier metal, resulting in a lower reliability of wires, particularly, deteriorated stress-migration and electro-migration. The residual tantalum oxide compound can also cause a stress-induced-voiding in which stresses produce voids in the wires.
Further, an extremely degraded adhesivity of copper metal layer 116 to the barrier metal would cause copper metal layer 116 to peel, resulting in defective wires and hence broken wires.
It is an object of the present invention to provide a method of manufacturing a semiconductor device which prevents a degradation in adhesivity of a copper metal layer to a barrier metal.
In the present invention, after forming a laminate metal film having a copper metal layer and a barrier metal, the laminate metal film is once immersed in a solution including an organic acid having at least one carboxyl group before a heat treatment, thereby removing from the laminate metal film an oxide which is the source of oxygen that diffuses during the heat treatment. It is therefore possible to prevent the barrier metal from reacting with oxygen and therefore suppress the generation of an oxide on the interface between the barrier metal and copper metal layer. Consequently, the method of the present invention can prevent degraded adhesivity of the copper metal layer to the barrier metal, and prevent deteriorated stress-migration and electro-migration for a wire using the laminate metal film. The method of the present invention can further prevent a stress-induced-voiding in the wire using the laminate metal film.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.